1. Field of the Invention
The present invention relates to a photosensitive polymer and a chemically amplified resist composition containing the same, and more particularly, to a photosensitive polymer having a main chain consisting of only norbornene-type alicyclic units, a resist composition containing the same, and a method of preparing the resist composition.
2. Description of the Related Art
As semiconductor devices become highly integrated, fine pattern formation is required in a photolithography process. Further, as the capacity of a semiconductor device increases to exceed 1 giga bit, a pattern size having a design rule of less than 0.2 xcexcm is required. Accordingly, there are limitations in using a conventional resist material with a KrF excimer laser (248 nm). Thus, new resist materials capable of being developed using an ArF excimer laser (193 nm) have been developed for a lithography process.
The resist materials used in the lithography process using the ArF excimer laser have several problems in being commercially used, compared to the conventional resist materials. The most typical problems are transmittance of a polymer and resistance to dry etching.
As the widely known ArF resist materials, (meth)acrylate polymers are generally used. In particular, the most typical resist material is a poly(methyl methacrylate-tert-butyl methacrylate-methacrylic acid) terpolymer system manufactured by IBM, Inc. However, such polymers have very weak resistance to dry etching.
Accordingly, to increase the resistance to dry etching, a polymer having a backbone composed of an alicyclic compound such as an isobornyl group, an adamantyl group or a tricyclodecyl group, is used. However, the resulting resist still exhibits weak resistance to dry etching.
Alternatively, in order to increase the resistance to dry etching, norbornene-type polymers having a main chain consisting of alicyclic units are used. The norbornene-type polymers are known to be incapable of radical polymerization by themselves. In this context, the norbornene-type polymers are prepared by alternating copolymerization with maleic anhydride. However, due to the introduction of maleic anhydride, the resistance to dry etching is lowered and the stability over time is poor, which shortens the shelf life of the polymer.
Accordingly, attempts have been made to attain copolymers having a main chain consisting of only norbornene-type units using addition polymerization employing a metallic catalyst such as palladium (see Joice P. Mathew et al., Macromolecules, 1996, 29(8), p 2755.). However, it is difficult to completely remove the metallic catalyst used for polymerization. Thus, in the case of using a resist composition obtained from the polymer, metallic components may remain on a wafer, which becomes a drawback in the use of the resist composition in manufacturing an electronic apparatus such as a semiconductor device.
To solve the above problems; it is a feature of a preferred embodiment of the present invention to provide a photosensitive polymer having a main chain consisting of only norbornene-type units so that sufficient resistance to dry etching can be attained.
It is another feature of a preferred embodiment of the present invention to provide a resist composition which contains the photosensitive polymer, which is free from a possibility that metallic components remain on a wafer, and which provides for excellent lithographic performance during a lithography process using an ArF excimer laser.
It is still another feature of a preferred embodiment of the present invention to provide a method of preparing a photosensitive polymer capable of synthesizing a polymer having a main chain consisting of only norbornene-type units without using a metal catalyst.
Accordingly, to achieve the above features, there is provided a photosensitive polymer represented by the following formula (1): 
wherein R1 is an acid-labile tertiary alkyl group, R2 is -butyrolactone-2-yl, xcex3-butyrolactone-3-yl, pantolactone-2-yl, mevalonic lactone, 3-tetrahydrofuranyl, 2,3-propylenecarbonate-1-yl or 3-methyl-xcex3-butyrolactone-3-yl, R3 is a hydrogen atom, methyl, ethyl or C3 to C20 alicyclic hydrocarbon group, and p/(p+q+r) is about 0.1 to about 0.8 (0.1xcx9c0.8), q/(p+q+r) is 0.2xcx9c0.8, and r/(p+q+r) is 0.0-0.4.
Preferably, the photosensitive polymer has a weight-average molecular weight of 3,000xcx9c100,000.
R1 is preferably t-butyl, 2-methyl-2-adamantyl, 1,2,3,3-tetramethyl-2-norbornyl, 2-methyl-2-decanyl, 2,3,3-trimethyl-2-norbornyl or 8-ethyl-8-tricyclo [5.2.1.02,6]decyl.
According to another aspect of a preferred embodiment of the present invention, there is provided a resist composition including (a) a photosensitive polymer represented by the following formula (2): 
wherein R1 is an acid-labile tertiary alkyl group, R2 is xcex3-butyrolactone-2-yl, xcex3-butyrolactone-3-yl, pantolactone-2-yl, mevalonic lactone, 3-tetrahydrofuranyl, 2,3-propylenecarbonate-1-yl or 3-methyl-xcex3-butyrolactone-3-yl, R3 is a hydrogen atom, methyl, ethyl or C3 to C20 alicyclic hydrocarbon group, and p/(p+q+r) is 0.1xcx9c0.8, q/(p+q+r) is 0.2xcx9c0.8, and r/(p+q+r) is 0.0xcx9c0.4, and (b) a photoacid generator (PAG).
The PAG is preferably included in an amount of about 1 to about 15% by weight based on the total weight of the polymer.
Examples of the PAG include triarylsulfonium salts, diaryliodonium salts, sulfonates or mixtures thereof.
The resist composition further includes an organic base.
Preferably, the organic base is contained in an amount of about 0.01 to about 2.0% by weight based on the total weight of the polymer.
Examples of the organic base include triethylamine, triisobutylamine, triisooctylamine, diethanolamine, triethanolamine or a mixture thereof.
Also, according to another aspect of a preferred embodiment of the present invention, there is provided a resist composition including (a) a polymer blend prepared by mixing at least two photosensitive polymers represented by formula (1), and (b) a photoacid generator (PAG).
According to still another aspect of a preferred embodiment of the present invention, there is provided a method of preparing a photosensitive polymer according to formula (1) above comprising the steps of reacting at least two different norbornene-type compounds having an ester group as a substituent in the presence of an initiator at a temperature of about 120 to about 150xc2x0 C. without a reaction catalyst.
The photosensitive polymer according to another preferred embodiment of the present invention has a main chain consisting of only norbornene-type units and can be prepared at a high yield without using a metallic catalyst. Also, the resist composition obtained from the polymer exhibits excellent adhesion.
Priority Korean Patent Application Serial No. 99-55836, filed Dec. 8, 1999, is incorporated herein in its entirety by reference.
A photosensitive polymer according to the present invention is represented by the following formula (1): 
wherein R1 is an acid-labile tertiary alkyl group which can be deprotected from the main chain of the polymer by the action of acid generated during exposure. For example, R1 is t-butyl or a substituted or unsubstituted C7 to C20 hydocarbon group, more particularly an alicyclic hydrocarbon group, such 2-methyl-2-adamantyl, 1,2,3,3-tetramethyl-2-norbornyl, 2-methyl-2-decyl, 2,3,3-trimethyl-2-norbornyl or 8-ethyl-8-tricyclo[5.2.1.02,6]decyl group.
Examples of R2 include xcex3-butyrolactone-2-yl, xcex3-butyrolactone-3-yl, pantolactone-2-yl, mevalonic lactone, 3-tetrahydrofuranyl, 2,3-propylenecarbonate-1-yl or 3-methyl-xcex3-butyrolactone-3-yl.
Examples of R3 include a hydrogen atom, methyl, ethyl or C3 to C20 alicyclic hydrocarbon.
Also, in Formula (1), p/(p+q+r) is 0.1xcx9c0.8, q/(p+q+r) is 0.2xcx9c0.8, and r/(p+q+r) is 0.0xcx9c0.4.
The above photosensitive copolymers cannot be synthesized by conventional radical polymerization or addition polymerization using a metallic catalyst. Even though polymerization is achieved by the conventional method, the molecular weight of the obtained polymer is very low, that is, about several hundreds, and the yield is very low.
Polymerization methods of a photosensitive polymer according to preferred embodiments of the present invention will now be described in detail.